1. Technical Field
The present invention relates to a lead pin for a package substrate, and more particularly, to a lead pin for a package substrate that includes a head part that has a round part formed on the lower end thereof, having a step part, and a connection pin that is vertically projected from the head pin.
2. Description of the Related Art
With the development of the electronics industry, various types of semiconductor packages have been manufactured. Recently, due to the increase in wiring density of a semiconductor package, a semiconductor package substrate in a Pin Grid Array (PGA) type in which a plurality of T-type lead pins are mounted has been widely used as a substrate that connects a package substrate on which an integrated circuit (IC) is mounted to a main board.
In a general package substrate, a pin insert type that a pin is inserted through a hole and a T-type lead pin that is attached to a package substrate by a soldering have been mainly used. The T-type lead pin has gradually become widespread due to limitation of the available area for the circuit configuration of the package substrate as compared to the pin insert type.
However, the T-type lead pin has disadvantages in that the lead pin is inclined and it is difficult to maintain uniform bonding strength when being mounted on the package substrate. In particular, as the use of lead has been recently limited in consideration of environmental effects due to the soldering, a soldering (Sn—Ag—Cu, and Sn—Sb) not using lead has been used, such that a melting temperature of the soldering becomes high.
As the melting temperature for soldering becomes high, a soldering for connecting lead pins that support lead pins is melted by reflow heat during a reflow process for mounting an IC chip on a package substrate, thereby causing inclination of the lead pins.
For example, several hundreds of lead pins mounted on a semiconductor are used in a CPU package substrate. If any one of them is inclined, the CPU itself cannot be mounted on a socket, such that the package substrate itself is regarded as a defective product.
Further, there is a possibility that voids are formed between the head part of the lead pin and a soldering when soldering the T-type lead pin according to the related art in addition to the inclination of the lead pin. Therefore, problems according to the related art will be described with reference to the accompanying drawings.
FIGS. 1 and 2 are configuration diagrams showing a bonding state of a lead pin according to the related art. As shown in FIGS. 1 and 2, after a solder paste 12 is applied to a pad part 11 of a package substrate 10, a lead pin 20 is mounted on the pad part 11 of the package substrate 10 so that the head part 21 of the lead pin 20 contacts the pad part 11 thereof.
Thereafter, when the plurality of lead pins 20 are mounted on the pad part 11 of the package substrate 10, a reflow process for mounting an IC chip on the package substrate 10 is performed and the IC chip is mounted and the plurality of lead pins 20 are coupled on the package substrate 10 by the reflow process.
However, when applying the solder paste 12 in order to bond the lead pins 20, bonding strength of the lead pins 20 may be degraded due to voids 13 generated in the solder paste 12. Further, the lead pins 20 may incline to one side of the lead pin 20 depending on the size of the void 13.
In addition, the solder paste (Sn95-Sb5, melting point 232 to 240° C.) for coupling the lead pins 20 has a higher melting point as compared to the solder paste (Sn96-Ag3.5-X solder, melting point 221° C.) for coupling the IC chips. However, in order to minimize thermal impact that is applied to the package substrate 10 during the reflow process, the heating time at the temperature of the melting point or more is controlled to be short, such that there is insufficient time to remove the voids 13 in the soldering. As a result, the melted surface of the solder paste 12 itself does not become uniform or tension with the lead pins 20 is generated due to the expansion of the voids 13, such that a bonding defect is caused due to the inclination of the lead pin 20 to one side.
Although not shown in FIGS. 1 and 2, the solder paste 12 applied to the pad part 11 of the package substrate 10 bulges along the upper portion of the head part 21 of the lead pin 20 due to high-temperature melting during the reflow process, such that the solder paste 12 directly contacts the pad of the socket when mounting the socket, thereby causing a short defect.